This disclosure relates generally to fusible circuits, and in particular but not exclusively, to externally programmed antifuses fabricated using metal-oxide-semiconductor (MOS) technology.
Fusible circuits are commonly used in integrated circuit devices to allow custom programming of an integrated circuit device after fabrication. For example, fusible circuits are commonly used in programmable logic devices. In addition, a fusible circuit can be used to repair a defective integrated circuit device by replacing a defective circuit with a spare (redundant) circuit, or to alter performance of the device by enabling/disabling circuitry on the device (e.g., trimming circuits).
There are many techniques to program fusible circuits. For example, a fuse or antifuse may be electrically programmed. Typically, each fusible circuit includes extra circuitry used to selectively provide relatively high voltages to alter a fusible element to create an open-circuit (i.e., a fuse) or create a short circuit (i.e., an antifuse). The extra circuitry tends to increase the size, complexity and cost of the integrated circuit device. Another technique is to use a high power laser to remove a portion of a conductor to create an open-circuit. However, even when properly focused on the desired location on the device, the high energy levels provided by the laser can damage nearby portions of the device. Thus, this laser cutting technique tends to be impractical for high-density integrated circuit devices. This technique usually requires front side access of the device, which is impossible for some packaged devices (e.g., C4 packaged devices). Yet another technique is to use a focused ion beam (FIB) to break or create connections. However, FIB tools are complex and expensive and can also damage nearby portions of the integrated circuit device.